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Combined study by optical diagnostics and Direct Numerical Simulation of the flame stabilization in

a Diesel-type spray

Fabien Tagliante

Thesis Director (IFPEN): Gilles Bruneaux Thesis co-Director (IFPEN): Christian Angelberger

Supervisor (IFPEN): Louis-Marie Malbec In collaboration with: Lyle M. Pickett (Sandia National Laboratories) &

Thierry Poinsot (CERFACS)

Ph.D. started in December 2015

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Scientific context of the flame stabilization under Diesel condition

What is the flame stabilization mechanism under Diesel condition?

Flame stabilization by auto-ignition

Experimental studies

Real physics

• Temporal and spatial resolution • Difficult to measure simultaneous quantities

• 3D-DNS too expensive to simulate a stabilized flame spray flame under Diesel condition

• RANS and LES combustion model assumption on the combustion regime

• Access to local values • Access to all the quantities

Edge-flames are involved in the flame stabilization process

CFD studies

The distance at which the flame stabilizes has a great impact on the soot production :

Pickett et al. SAE 2005-01-3843

Krisman et al. PCI 36 (2017) 3567–3575

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Scientific context of the flame stabilization under Diesel condition

What is the flame stabilization mechanism under Diesel condition?

Flame stabilization by auto-ignition

Experimental studies

Real physics

• Temporal and spatial resolution • Difficult to measure simultaneous quantities

• 3D-DNS too expensive to simulate a stabilized flame spray flame under Diesel condition

• RANS and LES combustion model assumption on the combustion regime

• Access to local values • Access to all the quantities

Edge-flames are involved in the flame stabilization process

CFD studies

The distance at which the flame stabilizes has a great impact on the soot production :

Pickett et al. SAE 2005-01-3843

Krisman et al. PCI 36 (2017) 3567–3575

Objective of my PhD: To contribute to a better understanding of the stabilization mechanisms of a Diesel-type flame combining optical diagnostics and CFD

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R [m

m]

Distance to nozzle [mm]

𝑻𝒂𝒎𝒃 = 𝟖𝟎𝟎𝑲; 𝝆𝒂𝒎𝒃 = 𝟏𝟒. 𝟖𝒌𝒈/𝒎𝟑; 𝑷𝒊𝒏𝒋 = 𝟏𝟓𝟎𝐌𝐏𝐚

• Broadband chemiluminescence (30 kHz) LOL detection • 355 LIF (6 kHz) detection of cool flame areas (formaldehyde species) • Schlieren images (30 kHz) Evolution of the gaseous jet envelope

Simultaneous and time-resolved optical diagnostics

3 simultaneous and time-resolved optical diagnostics

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Focus on the high-temperature flame

OH* chemiluminescence at 60 kfps to track the high-temperature flame

t = 5233 µs

10

0

10

t = 5700 µs

t = 6000 µs

Distance to nozzle [mm]

0 10 20 30 40

R [

mm

]

10

0

10

0

𝐋𝐎𝐋

t = 5216 µs

10

0

Camera :

OH* chemiluminescence

Injector

300-330nm filter

Mirror

Intensifier

Beam splitter

◘

Mirror

Downstream evolution of the LOL Evolution B

t = 5700 µs

t = 6000 µs

Distance to nozzle [mm]

0 10 20 30 40

10

0

10

0

𝐋𝐎𝐋

Auto-ignition Event A

t = 5233 µs

10

0

10

R [

mm

]

t = 5216 µs

10

0

F. Tagliante, L-M. Malbec, G. Bruneaux, L.M Pickett, C. Angelber, Experimental study of the stabilization mechanism of a lifted Diesel-type flame using combined optical diagnostics and laser-induced plasma ignition, Combustion and Flame 197 (2018) 215-226.

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Numerical setup

Non-simulated area due to: • Very high Reynolds number • Two phase flow

Objective: To reproduce the 𝛼 test conditions to distinguish the stabilization mechanisms thanks to local values

• 2D-DNS • Gaseous injection + Synthetic turbulence

• Chemistry: 28 species transported

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Numerical setup

Non-simulated area due to: • Very high Reynolds number • Two phase flow

Objective: To reproduce the 𝛼 test conditions to distinguish the stabilization mechanisms thanks to local values

• 2D-DNS • Gaseous injection + Synthetic turbulence

• Chemistry: 28 species transported

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2D DNS

𝑧𝑠𝑡 = 0.048

H𝑒𝑎𝑡 𝑅𝑒𝑙𝑒𝑎𝑠𝑒 = 4𝑒11 𝑊/𝑚3

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LOL tracking with the reaction zone topologies identification

LOL tracking (DNS results)

Time [ms]

LO

L [

m]

Event A

Ev. B

The DNS allows to: • Isolate local reaction zone topologies

identified at the lift-off Focus on auto-ignition: Event A

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Reaction zone topologies: isolated auto-ignition

𝑧𝑠𝑡 = 0.048

H𝑒𝑎𝑡 𝑅𝑒𝑙𝑒𝑎𝑠𝑒 = 4𝑒11 𝑊/𝑚3

Isolated auto-ignition (AI-I)

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Reaction zone topologies: auto-ignition assisted by burnt gases

Auto-ignition assisted by burnt gases (AI-BG)

𝑧𝑠𝑡 = 0.048

H𝑒𝑎𝑡 𝑅𝑒𝑙𝑒𝑎𝑠𝑒 = 4𝑒11 𝑊/𝑚3

600 2250 T [K]

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LOL tracking with the reaction zone topologies identification

LOL tracking (DNS results)

Time [ms]

• Like in the experimental study, two main stages are observed, stage A and B:

o Event A is attributed to isolated auto-ignition (AI-I) or auto-ignition assisted by burnt gases (AI-BG)

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• Like in the experimental study, two main stages are observed, stage A and B:

o Evolution B: triple flame (TF) or lean/rich reaction zone (L/R RZ)

o Event A: isolated auto-ignition (AI-I) or auto-ignition assisted by brunt gases (AI-BG)

LOL tracking with the reaction zone topologies identification

LOL tracking (DNS results)

𝑈𝑋,𝑓𝑙𝑜𝑤,𝐿𝑂 = 1 m/s

𝑈𝑋,𝑓𝑙𝑜𝑤,𝐿𝑂 = 34 m/s

Time [ms]

governed by the flow velocity

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Conceptual model of flame stabilization

F. Tagliante, T. Poinsot, L. M. Pickett, P. Pepiot, L-M. Malbec, G. Bruneaux, C. Angelberger, A conceptual model of flame stabilization mechanisms for a lifted Diesel-type flame based on Direct Numerical Simulation and experiments . Submitted to Combustion and Flame in October 2018.

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Thank you for your attention